nRuleItems returns numbers of items (each item corresponds to one field of output data) in the specified rule.
C/C++/C#
int nRuleItems(RULE_HANDLE handle)
Returns number of items (>=0) in success or -1 otherwise.

GetRuleItem returns handle for the specified rule's item.
C/C++/C#
ITEM_HANDLE GetRuleItem(RULE_HANDLE handle, int idx)
'idx' is zero based index of the item to be retrieved.

SetRuleItem replaces existing rule item by specified
C/C++/C#
int SetRuleItem(RULE_HANDLE handle, int idx, ITEM_HANDLE item)
'idx' is zero based index of the item to be replaced.

COM object offers "RuleItem" integer property for described functions. You should not use "SetRuleItem" and "GetRuleItem" functions directly in this case.

RemoveRuleItem removes specified rule item from the list.
C/C++/C#
int RemoveRuleItem(RULE_HANDLE handle, int idx)
'idx' is zero based index of the item to be removed.

AddRuleItem appends new item to the specified rule
C/C++/C#
int AddRuleItem(RULE_HANDLE handle, ITEM_HANDLE item)